RE: [xtm-wg] XTM-ISS Important XLink difference in DTDs

["Kal Ahmed" <kal@ontopia.net>]

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Philip Rutherford wrote:

>
> It seems to me that there is an important XLink difference between
> STEP's DTD (tm.dtd) and Michel Biezunski's DTD (mb.dtd). In STEP's DTD
> the <topic> element is the extended XLink and it contains <occurs>
> elements which are the XLink locators. In Michel's DTD however it is the
> <occurs> element that would be the extended XLink, and it contains
> <locator> elements which are then the XLink locators.
>
> For my own application of XTMs which is in describing web site structure
> I prefer Michel's DTD because it gives greater ability to add resource
> meta data to each <occurs> element. The example below uses Michel's DTD
> to describe a simple web site containing two documents: welcome.html and
> contact.html. This DTD allows separate descriptions of the two documents
> to be added using the XLink resource type element, as can be seen below.
>
[example removed for brevity]
>
> Below is the same example using STEP's DTD. Without adding the
> complexity of <arc> elements there is no way of defining which resource
> description goes with which locator and thus this information would be
> lost in the interchange.
>
[example edited out again]

But there are facets to do the same job - in fact the facet can be used to
associate any arbitary meta-data with each resource.

> Even though Michel's DTD may add an extra element to the ISO standard I
> think it makes the definition more powerful when used in conjunction
> with XLink especially where a topic has many occurrences. It also gives
> occurrences the same XLink status as associations which seems to make
> more sense in terms of symmetry and may also make it easier to implement
> in practical situations.
>
> What are other peoples feelings on this?
>

My only problem with this approach is that the topic is demoted from its
status as being a link element. The reason that I find this a problem is
that if I were to process an instance of tm.dtd with an XLink processor, it
would equate each topic to an extended link and would group the occurrences
as locators of the link. In other words, the XLink processor - without any
knowledge of topic maps - correctly interprets the <topic> element as some
sort of aggregate link. If the XLink processor were to process an instance
of mb.dtd, it is only the containement provided by the <topic> element that
gives any hint as to the relationship between the individual extended links
(<occurs>). I like the idea that a less well-informed processor could still
look at an XTM instance and make some 'true' statements about it.

Of course, it could be argued that by forcing you to use facets to specify
meta-data about the resource, the tm.dtd has 'hidden' some information from
a standard XLink processor. But my feeling is that keeping the structural
nature of the topic link is of a higher priority. Of course, if there is
some way to do both that would be really cool... ;-)

Cheers,

Kal
-------------------------------------------
Kal Ahmed, Principal Consultant, Ontopia AS
kal@ontopia.net
-------------------------------------------


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